Sound reproducer



March 5, 1929. H. c. HAYES I SOUND REPRODUCER Filed Jan. 1927 alikoz vwq Patented Mar. 5, 1929.

UNITED STATES HARVEY G. HAYES, 01E WASHINGTON, DISTRICT OF COLUMBIA.

SOUND REPRODUCER.

Application filed January 4, 1927. Serial No. 158,954.

My invention relates broadly to apparatus for imparting Vibrations to sonic diaphragms and more particularly to apparatus for imparting vibrations to tensioned sonic diaphragms. My invention is of particular application in an electromagnetic device where both a push and a pull thrust is exerted on a diaphragm in response to fluctuations of current acting in the energizing coils.

The object of my invention is to construct sound reproduction units that are more sensitive to small current fluctuations than those in present use. p

Another object of my invention is the con- 5 struction of a sonic reproduction unit that gives a more faithful translation of the current fluctuations in the electrical circuit than "is now obtained.

Further objects of my invention will appear more fully hereinafter.

Faithful reproduction of sound over a wide range of frequencies, such as is desired in telephones and loud speakers, demands that the vibrations of the diaphragm producing the 2 sound he of a forced type, that is, the resonant frequency of the diaphragm should be outside the range of frequencies that the diaphragm iscalled upon to reproduce.

This condition normally requires that large restoring forces be brought into action when the diaphragm or other moving parts are displaced from their position of equilibrium.

The mass required to give the necessary rigidity in the instruments now in use, tends to make the inertia. of the moving parts so great that the sensitivity of the apparatus is unnecessarily low. I have discovered that I can overcome this inherent difliculty by making the restoring force of the moving parts great in proportion to their mass. This I have accomplished by the utilization of a tensioned armature, the restoring force of which is independent of the mass and may be increased at will.

My invention consists substantially in the construction, combination and arrangement of parts associated therewith as will be more fully hereinafter set forth, as shown by the accompanying drawing and finally pointed out in the appended claims.

Reference is to be had to the accompanying drawing forming a part of this specification, which shows a diagrammatic arrangement of the parts of a sound reproducer unitconstructed in accordance with my invention.

The device consists of two telephone magnets of the bipolar type so mounted that the unlike poles 3 and 5, and, 4 and 6, of the two magnets are directly opposite each other. Each of the telephone magnets consists of a permanent magnet and a lurality of electromagnets. For example t 1e lower telephone magnet consists of a permanent magnet 7 and two electromagnets 1. Each of the electromagnets consists of an L-shaped soft iron member with the angle of the L placed upon one of the poles of the permanent magnet and one leg of each L extending toward the electromagnet upon the other pole of the permanent magnet. Upon each one of the electromagnets is wound a coil of wire 13. The upper and lower telephone magnets are so spaced that a tensioned armature 14 of high permeability and low hysteresis and eddy current losses can be centered between the poles 3 and 4 of magnet 1 and the poles 5 and 6 of magnet 2. I Y

The proper selection of the magnets 7 and 8 would be such that they will be of sufiicient strength to prevent the telephonic currents in the electromagnets 1 and 2 from reversing their polarity and alsoof such strength that the magnetic flux between the poles 3 and 5 and the poles 4 and 6 will be equal. Also the strength of the poles 9 and 10 of the magnet 8 will be equal to the strength of the poles 12 and 11 of the magnet 7 respectively. When the magnets are mounted in the manner shown the magnets 1 form a link for the magneticfiux between the poles 11 and 12 of permanent magnet 7. In a similar manner, magnets 2 form a link for the magnetic flux between the poles of magnet 8.

The operation of my device depends upon shunting through the armature 1Q a portion of the magnetic flux created in one or the other of magnets 1 and 2. The amount so shunted is dependent upon the strength of the current through the coils 13 of the two magnets 1 and 2. The direction of the current in the coils 13 determines which of the permanent magnets 7 or 8 has its flux linked with the armature.

To produce this effect the coils 13 of the two magnets 1 and 2 are connected in series or in parallel in such a way that a current passing through the coils will strengthen the magnetic flux of one magnet, for example 1, and weaken the magnetic flux of the other magnet, for example 2. The particular effect which prevails upon the magnets at a single instant depends upon the direction of the ture 14, across the small air gap between the armature and pole 5 of magnet 2 through the metal of magnet 2 to pole 9 of permanent magnet 8, through magnet 8 to pole 10 of magnet 8, through the metal of magnet 2 to pole 6 of magnet 2, across the small air gap between the pole 6, and the armature, perpendicularly through the armature and across air gap between the armature 14 and pole 4 of magnet 1, through the metal of agnet- 1 to pole 12 of permanent magnet 7, through magnet 7.to pole 11 of magnet 7, through the metal of magnet 1 and to pole 3 of magnet 1.

, When'the armature is exactly centered 1n the gaps between the magnets by the adjustment of the tension thereon which, in the em- 'bodiment herein disclosed is accomplished by 'the means of the thumbscrew 19 which is threaded into the armature supporting member 20 which consists of non-magnetic matetion, that is there is no magneto-motive force tending to cause flux in the armature 14. It will be seen that when the armature is so posi tioned it is in a critically unstable condition.

It is. to be understood that the showing in the drawings of the supporting means and the thumbscrew adjustment for the tension upon the armature 14 is but oneembodiment of such means, and that any type of tensioning and supporting means may be used without departing from the spirit of my invention and without departing from the scope of the appended claims. If, from its centered position, the armature is mechanically displaced slightly toward one magnet for example 7 then the air gaps between the armature and the two poles 3 and 4 are less than those between the armature and the two poles 5 and 6 and a certain portion of the flux of magnet 7 will pass through the armature in preference to passing across the gaps to poles 5 and 6 because of the diminished reluctance given by this path along the armature. This linkage of flux between the armature and poles 3 and 4 causes the armature to be attracted toward these poles more than it is attracted toward poles 5 and 6 with the resultant pull toward magnet 7 increasing rapidly as the armature approaches pole 3 and 4.

This movement continues until the tensional restoring forces exerted upon the armature equals the pull of the magnet upon the armature.

The varying flux in the electromagnets produced by the varying currents flowing in the coil 13 produces the equivalent of this mechanical displacement. Assuming that the armature 14 is again in its centered position, and that the first half cycle of an alternating current traverses the coils 13. This flow of current produces an increase in the attraction of the arplature toward the electromagnets 1, for example, and a decrease in the attraction of the magnets 2 for the armature 14. This slight force is sufiicient to displace the armature from its centered position. A portion of the flux from the ermanent magnet 7 then passes longitudinal y through the armature 14 due to the decreased reluctance of this path. This change in flux then increases as the armature moves away from its centered position to the position in which the tension exerted upon the armature counterbalances the attraction of the magnet for the armature. Then when the other half cycle of alternating current passes through the coil 13 the attraction of the electromagnets 1 for the armature 14 is decreased and the attraction of the elcctromagnets 2 iis increased. This change in flux together with the restoring tensional force causes the armature 14 to leave-the position just described and pass through the centered position of unstable equilibrium to a position in close proximity to the clectromagnets 2 where the flux from the permanent magnet 8 exerts a pull upon the armature 14 that is equal to the restoring forces exerted upon the armature by the tension placed thereon. As the cycles of the current in the coils 13 are repeated the vibrations of the diaphragm 17 are producedby the vibrations of the armature 14.

Since the tensioned armature has as great restoring force per unit displacement as the heavier untensioned ones in present use, and in many cases has a greater restoring force per unit displacement than the heavier untensioned ones, the time required to build u or vary the amplitude or frequency of the lig ter armature will be much less with the result that the current fluctuations will give a more faithful reproduction of the sound that it is desired to produce.

Since the sensitivity of the magnetic driver becomes greater as the design and adjustments are so arranged that the comparatively small current fluctuations through the coils produce a maximum change inmagnetic' flux linkage betweenthe fixed and movable parts of the magnetic circuit, the maximum sensitivity is reached when the air-gap between the armature and each pair of poles is made only of sufiicient size for the armature to This normally reduces the clearance between armature and pole pieces to 7 to 10 thousandths of an inch. The reluctance of the magnetic circuit (including for each set of coils, the soft iron pole-pieces, the armature and three small air gaps) is then sufiiciently i low to permit the change in ampere turns or demagnetize the permanent magnets, the

purpose of which is to keep the polarity of poles 5 and 3 and G and 4 constant.

It will be understood that the above description and accompanying drawings co1n prehend only the general and preferred embodiment of my invention and that minor detail clmnges in construction and arrangement of parts may be made within the scope of the appended claims and without sacrificing any of the advantages of my invention.

I claim as follows:

1. In combination with a tensioned armature, a permanent magnet disposed upon one side of the armature. a. like permanent magnet disposcd upon the other side of the armature, the unlike poles of the two magnets disposed opposite to each other, the lux between the two magnets passing perpendicularly through the armature, and a plurality of electromagnets disposed between the permanent magnets and the armature.

2. In combination with a tensioned armature, a permanent magnet disposed upon one side of the armature, a like permanent magnet disposed upon the other side of the armature, the unlike poles of the two magnets disposed opposite to each other, the flux between the two magnets passing perpendicularly through the armature, and a plurality of electromagnets disposed between the permanent magnets and the armature one electroinagnet disposed between one permanent magnet and the armature, the other electromagnet disposed between the other permanent magnet and the armature.

3. In combination with a tensioned armature, a permanent magnet disposed upon one side of the armature, a like permanent magnet disposed upon the other side of the armature, the unlike poles of the two magnets disposed opposite to each other, the flux between the two magnets passing perpendicularly through the armature, and a plurality of electromagnets disposed between the permanent magnets and the armature one electromagnet disposed between one permanent magnet and the armature, the other electromagnet disposed between the other permanent magnet and the armature, the elect romagnets being 7 so wound that a flow of current through the coils of the electromagnets increases the efi'ect upon the tensioned armature of one of the permanent magnets and decreases the'eflfect of the other permanent magnet.

HARVEY C. HAYES. 

